Antigelling agent for hydrocarbon mixture containing conjugated diene and method of preventing clogging of apparatus for separating and purifying the mixture

ABSTRACT

An Anti-gelling agent for a hydrocarbon mixture containing a conjugated diene, which comprises (a) at least one compound selected from the group consisting of compounds having an NO radical in the molecule, and precursor compounds capable of forming an NO radical, (b) a phosphorus-containing compound, and (c) at least one compound selected from the group consisting of heterocyclic aldehydes, aromatic aldehydes and condensates of these aldehydes. Clogging in an apparatus for separating and refining a hydrocarbon mixture containing a conjugated diene can be prevented by adding the anti-gelling agent in the apparatus.

TECHNICAL FIELD

This invention relates to a method of preventing clogging of anapparatus for separating and refining a hydrocarbon mixture containing aconjugated diene, and an anti-gelling agent for the hydrocarbon mixture.More specifically, it relates to an anti-gelling agent used forpreventing clogging and a method of preventing clogging in an apparatus,which are used for separating and refining unsaturated hydrocarbons suchas ethylene, propylene, butene, butadiene or isoprene from a hydrocarbonmixture containing hydrocarbon compounds having at least two carbonatoms which mixture is produced by removing, for example, methane,hydrogen and nitrogen from a cracker gas of a thermal cracker or arefinery gas from a refinery, wherein clogging of a distillation column,a reboiler or a piping is prevented and the reduction of heat efficiencyis minimized.

BACKGROUND ART

Conjugated dienes such as butadiene and isoprene tend to be polymerizedalone or copolymerized with other copolymerizable unsaturated compoundat a step of distillation, extractive distillation, extraction,hydrogen-treatment, hydrogenation purification or heat treatment, orduring storage, transportation or processing.

Conjugated dienes are contained, for example, in a C4 hydrocarbonfraction, a C5 hydrocarbon fraction, a hydrocarbon mixture containinghydrocarbon compounds having at least two carbon atoms, such as thatproduced by removing mathane, hydrogen and nitrogen from a cracker gasfrom a thermal cracker or a refinery gas from a refinery, a hydrocarbonmixture containing hydrocarbon compounds having at least three carbonatoms, such as that produced by separating and refining ethylene forexample, by low-temperature fractional distillation, and a hydrocarbonmixture containing hydrocarbon compounds having at least six carbonatoms, such as that produced by removing a C4 hydrocarbon fraction and aC5 hydrocarbon fraction. In an apparatus for separating and refiningthese hydrocarbon fractions and hydrocarbon mixtures, a column or tank,a piping, a heat exchanger and the like of the apparatus are liable tobe clogged with a polymer deposited thereon. The polymer is believed tobe produced by polymerization or copolymerization of the conjugateddienes. Therefore, operation of the apparatus must be regularly orirregularly stopped for cleaning the inside thereof to remove thedeposited polymer.

Thus, it is desired to prevent polymerization of conjugated dienes andto minimize clogging of a deposited polymer in an apparatus ofseparating and refining a hydrocarbon mixture containing conjugateddienes. As the method of preventing polymerization of conjugated dienes,there have bee proposed, for example, a method of distilling a C5hydrocarbon fraction in the presence of a di-lower-alkyl-hydroxylaminein Japanese Unexamined Patent Publication (hereinafter abbreviated to“JP-A”) No. S50-112304, a method of effecting an extractive distillationwhile furfural and a condensate of furfural are made present in anextraction medium in JP-A S56-81526 or Japanese Examined PatentPublication (hereinafter abbreviated to “JP-B”) No. S43-20281, a methodof extractive distilling a conjugated diene hydrocarbon while apolymerization inhibitor or a chain transfer agent is made present in anextraction medium in JP-B S47-41323 or JP-B S45-19682, and a method ofprohibiting polymerization of a conjugated diene hydrocarbon byincorporating therein an organic phosphate ester compound in JP-BS49-6886 or JP-S49-7126.

According to the heretofore proposed polymerization-preventing methodsand polymerisation inhibitors, even though the polymerization inhibitoris incorporated in a sufficient amount, the problem of clogging in aseparating and refining apparatus, especially in a vessel wherein ahydrocarbon mixture is exposed to a high temperature, such as anevaporator or a distillation column, cannot completely be solved.

DISCLOSURE OF THE INVENTION

An object of the present invention is to provide an anti-galling agentfor preventing clogging and a method of preventing clogging in aseparating and refining apparatus for a hydrocarbon mixture, wherebyformation of gel at a high temperature is reduced, staining within theapparatus and clogging of piping and other vessels are avoided, andreduction of heat efficiency in minimized over a long period of time byincorporating a minor amount of the anti-gelling agent.

To achieve the above-mentioned object, the present inventor madeextensive researches and found it important to prevent not onlypolymerization of a conjugated diene but also gelling of a polymer tocompletely solve the problem of clogging in piping and other vessels.The present inventor further found that the above-mentioned object canbe achieved by feeding an anti-gelling agent containing a compoundhaving an NO radical in the molecule or a precursor compound capable offorming an NO radical, a phosphorus-containing compound, and furfural orits condensate, into an apparatus for separating and refining ahydrocarbon mixture.

Thus, in accordance with the present invention, there is provided ananti-gelling agent for a hydrocarbon mixture containing a conjugateddiene, which comprises (a) at least one compound selected from the groupconsisting of compounds having an NO radical in the molecule, andprecursor compounds capable of forming an NO radical, (b) aphosphorus-containing compound, and (c) at least one compound selectedfrom the group consisting of heterocyclic aldehydes, aromatic aldehydesand condensates of these aldehydes.

In accordance with the present invention, there is further provided amethod of preventing clogging in an apparatus of separating and refininga hydrocarbon mixture containing a conjugated diene, which comprisesadding into the apparatus (a) at least one compound selected from thegroup consisting of compounds having an NO radical in the molecule, andprecursor compounds capable of forming an NO radical, (b) aphosphorus-containing compound, and (c) at least one compound selectedfrom the group consisting of heterocyclic aldehydes, aromatic aldehydesand condensates of these aldehydes,

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an apparatus for separating andrefining a C4 fraction from a hydrocarbon mixture;

FIG. 2 is a schematic diagram of an apparatus for separating andrefining a C5 fraction from a hydrocarbon mixture; and

FIG. 3 is a schematic diagram of an apparatus for separating andrefining C2 to C9 fractions from a hydrocarbon mixture.

BEST MODE FOR CARRYING OUT THE INVENTION

The anti-galling agent of the present invention comprises (a) at leastone compound selected from the group consisting of compounds having anNO radical in the molecule, and precursor compounds capable of formingan NO radical, (b) a phosphorus-containing compound, and (c) at leastone compound selected from the group consisting of heterocyclicaldehydes, aromatic aldehydes and condensates of these aldehydes,

Compound (a)

Compound (a) is at least one compound selected from compounds having anNO radical in the molecule, and precursor compounds capable of formingan NO radical, and it includes inorganic compounds and organiccompounds. As examples of such compounds, the following compounds (1) to(7) can be mentioned.(1) N,N-dialkylhydroxylamines Represented by the Formula (I):

wherein R¹ and R² independently represents a straight chain, branched orcyclic alkyl group having 1 to 10 carbon atoms.

The alkyl group preferably has 1 to 6 carbon atoms. As specific examplesof the alkyl group, there can be mentioned methyl, ethyl, propyl,isopropyl, butyl, pentyl and cyclohexyl groups. As a preferable specificexample of the N,N-dialkylhydroxylamine, there can be mentionedN,N-diethylhydroxylamine (DEHA).

(2) Nitroxyl Compounds of a Steric Hindered Amine as Described in JP-BS60-237065 (a Compound Having an NO Radical in the Molecule)

The nitroxyl compounds (also called as N-oxyl or nitroxide is a freeradical having an unpaired electron, represented by the followingformula (II):

wherein the nitrogen atom is bonded directly with two carbon atomshaving four substituents, each of E¹, E², E³ and E⁴ independentlyrepresents an organic group, and T represents an organic group neededfor forming a five-membered or six-membered ring.

A preferable example of E¹, E², E³ and E⁴ is a methyl group. As specificexamples of the nitroxyl compound, there can be mentioned4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl,4-oxo-2,2,6,6-tetramethylpiperidin-1-oxyl,4-benzoyloxy-2,2,6,6-tetramethylpiperidin-1-oxyl,3-carbamoyl-2,2,5,5-tetramethylpyrrolidin-1-oxyl,N-(1-oxyl-2,2,6,6-tetramethylpiperidin-4-yl)-ξ-caprolactam,3-oxyl-2,2,4,4-tetramethyl-7-oxa-3,20-diazaspiro[5.1.11.2]heneicosan-21-on,4-aza-3,3-dimethyl-4-oxyl-1-oxaspiro[4.5]decane and2,4,4-trimethyl-2-phenyloxazolidine-3-oxyl,

(3) Hydroxylamine Compounds Corresponding to Nitroxyl Compounds of aSteric Hindered Amine as Described in JP-B S60-237065

The above-mentioned hydroxylamine compound is a precursor compound ofcapable of forming an NO radical (free radical) in situ in a systemhaving added therein a polymerization inhibitor, and is expressed by thefollowing formula (III):

wherein the nitrogen atom is bonded directly with two carbon atomshaving four substituents, each of E¹, E², E³ and E⁴ independentlyrepresents an organic group, and T represents an organic group neededfor forming a five-membered or six-membered ring,

A preferable example of E¹, E², E³ and E⁴ is a methyl group. As specificexamples of the hydroxylamine compound, there can be mentioned1,4-dihydroxy-2,2,6,6-tetramethylpiperidine,4-benzoyloxy-1-hydroxy-2,2,6,6-tetramethylpiperidine,di-(1-hydroxy-2,2,6,6-tetramethylpiperidin-4-yl) sebacate andN-(1-hydroxy-2,2,6,6-tetramethylpiperidin-4-yl)-ξ-caprolactam.

(4) Nitrogen Oxides Having a Stable Free Radical and Precursors Capableof Forming a Stable Free Radical in situ, as Described in JP-B H4-26639.

The nitrogen oxides having a stable free radical (more specifically, afree radical existing for a prolonged period such that it is capable ofbeing detected in a static system by an ordinary spectroscopicexamination; half-life being usually at least one year) includes, forexample, di-t-butyl nitroxide, piperidinyl-1-oxy compounds,pyrrolidin-1-oxy compounds and pyrrolin-1-oxy compound. As specificexamples of the piperidinyl-1-oxy compounds, there can be mentioned4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxy,4-oxo-2,2,6,6-tetramethylpiperidine-1-oxy and2,2,6,6-tetramethylpiperidine-1-oxy.

The precursors capable of forming a stable free radical in situ include,for example, nitron, nitroso, thioketone, benzoquinone andhydroxylamine. The precursors further include nitrosophenylhydroxylamine and its ammonium salt.

(5) Reaction Products of N,N-di-lower-alkylhydroxylamine with an OrganicAcid as Described in U.S. Pat. No. 3,371,124 and JP-B S41-17458

The reaction products include, for example, salts of oxalic acid withthe above-mentioned N,N-dialkylhydroxylamine [e.g.,bis(diethylhydroxylamine)oxalate], and salts of an oxyacid orpolycarboxylic acid with N,N-di-lower-alkylhydroxylamine as described inJP-B S41-17458.

As specific examples of the lower alkyl group, there can be mentionedmethyl, ethyl, propyl, isopropyl, butyl and hexyl groups. As specificexamples of the organic acid, there can be mentioned oxalic acid, lacticacid, tartaric acid, citric acid, malic acid, malonic acid, sucoinioacid, glutaric acid, adipic acid, pimelic acid, sebacic acid and azelaicacid.

An specific examples of the salts of N,N-di-lower-alkylhydroxylamine,there can be mentioned diethylhydroxylammonium citric acid salt,bis(diethylhydroxylammonium)tartaric acid salt,bis(diethylhydroxylammonium)adipic acid salt andbis-dibutyl-hydroxylamine sebacic acid salt.

(6) Hindered amine compounds having an N-hydrocarbyloxy substituent asdescribed in JP-A H4-233905; heterocyclic compounds such asphenothiazine as described in JP-A H4-233906; primary, secondary ortertiary hydroxylamine compounds; hindered amine compounds having anN-oxycarbamoyl substituent as described in JP-A H4-233907; and N—OHcompounds as described in JP-A H4-288302, such asN-(1-hydroxy-2,2,6,6-tetramethylpiperidin-4-yl)caprolactam,bis(1-hydroxy-2,2,6,6-tetramethylpiperidin-4-yl)sebacate,1-hydroxy-2,2,6,6-tetramethylpiperidin-4-yl benzoate and1-hydroxy-2,2,6,6-tetramethylpiperidin-4-yl acryalte.

Representative examples of these compounds are those which arerepresented by the following formulae (IV) and (V):

wherein the nitrogen atom is bonded directly with two carbon atomshaving four substituents, each of E¹, E², E³ and E⁴ independentlyrepresents an organic group, and X represents a divalent connectinggroup.

wherein the nitrogen atom is bonded directly with two carbon atomshaving four substituents, each of E¹, E², E³ and E⁴ independentlyrepresents an organic group, and X represents a divalent connectinggroup.

In formulae (IV) and (V), a preferable example of E¹, E², E³ and E⁴ is amethyl group, and a preferable example of X is represented by theformula:—COO—(CH₂)_(n)—COO— (n=1-20)As specific example of the compound having such divalent connectinggroup X, there can be mentionedbis(1-oxy-2,2,6,6-tetramethylpiperidin-4-yl)sebacate represented by thefollowing formula (VI):

(7) Nitric Acid Salt

A nitric acid salt such as sodium nitrite (NaNO₂) is an inorganiccompound precursor capable of forming an NO radical in situ in a systemhaving added therein a polymerization inhibitor. Sodium nitrite isespecially effective when it is used in combination with an inorganicphosphorus-containing compound, mentioned below, such as sodiumdihydrogenphosphate, or a phosphate ester surface active agent ortris(nonylphenyl)phosphite.

Among the above-mentioned compounds (a), compound (1) overlaps withcompound (6). Most of the above-mentioned compounds (a) are generallyknown as a premature polymerization inhibitor. However, the presentinventor's research revealed that these compounds (a) exhibit poorpolymerization inhibiting activity for many monomers includingconjugated diene monomers. In the present invention, compound (a) ischaracterized as being used in combination with a phosphorus-containingcompound (b),

Phosphorus-containing Compound (b)

The phosphorus-containing compound is not particularly limited, andincludes, for example, (i) a phosphoric acid compound selected fromphosphoric acid, phosphonic acid, phosphinic acid, diphosphonic acid,hypophosphoric acid, diphosphoric acid, tripolyphosphoric acid andmataphosphoric acid, (ii) an ester of the phosphoric acid compound,(iii) an alkali metal salt or an ammonium salt of the phosphoric acidcompound, (iv) a compound prepared by introducing an ester bond plus analkali metal bond or an ammonium salt bond into the phosphoric acidcompound, (v) a phosphine compound, and (vi) a hexaalkylphosphorustriamide. As specific examples of these phosphorus-containing compounds,there can be mentioned the following compounds.

(i) Phosphoric Acid Compound

(1) Phosphoric Acid

(2) Phosphonic Acid (Phosphorous Acid)

Phosphonic acid is a dibasic acid, shown in the left of formula (2),having a P—H bond, whose oxidation number is 3. Phosphonic acid isconsidered to have a tautomer, shown in the right of formula (2).

(3) Phosphinic Acid (Hypophosphorous Acid)

Phosphinic acid is a monobasic acid, shown in the left in formula (3),whose oxidation number is 3. Phosphinic acid is considered to have atautomer, shown in the right in formula (3).

(4) Diphosphonic Acid (Diphosphorous Acid)

(5) Hypophosphoric Acid

(6) Pyrophosphoric Acid (Diphosphoric Acid)

(7) Tripolyphosphoric Acid (Triphosphoric Acid)H₅P₃O₁₀  (7)

(8) Metaphosphoric Acid

wherein n is usually in the range of 0 to 14.(ii) Ester of Phosphoric Acid Compound

(1) Alkyl Dihydrogenphosphate

wherein R includes hydrocarbon groups such alkyl, phenyl and alkylphenylgroups, and further includes hydrophobic groups such as polyethyleneoxide and alkylphenyl polyethylene oxide groups. This definition for Ris the same in the following compounds.

(2) Dialkyl Hydrogenphosphate

(3) Trialkyl Phosphate

Besides the above compounds (1), (2) and (3), the ester of a phosphoricacid compound further includes, for example, phosphonic acid asters suchas dimethyl phosphonate, diethyl phosphonate, triethyl phosphonate,triisopropyl phosphonate and triphenyl phosphonate, and metaphosphoricacid esters.

The phosphonic acid asters are phosphorus-containing compoundsrepresented by the following formulae (12), (13) and (14);HP(O)(OH)(OR)  (12)HP(O)(OR)₂  (13)P(OR)₃  (14)

As specific examples of the ester of a phosphoric acid compound, therecan be mentioned triphenyl phosphate represented by the formula (15):

and tris(nonylphenyl)phosphite represented by the formula (16):(C₉H₁₀—C₈H₄—O)₃P  (16)

The ester of a phosphoric acid compound, which has a hydrophobic group,includes various phosphoric acid ester surface active agents. Of thephosphoric acid ester surface active agents, those which are generallyused as a corrosion preventive are especially preferable because theyfunction as an inhibitor for a popcorn polymer and a rubbery polymer aswell as a corrosion preventive, The phosphoric acid ester surface activeagent includes, for examples an alkyl dihydrogenphosphate represented bythe formulae (17):

wherein R¹ is an alkyl group having usually 7 to 18 carbon atoms,especially 8 or 9 carbon atoms, and n is an average addition mole numberof usually 1 to 18, in many cases 2 to 8, a dialkyl hydrogenphosphaterepresented by the formula (18):

wherein R¹ is an alkyl group having usually 7 to 16 carbon atoms,especially 8 or 9 carbon atoms, and n is an average addition mole numberof usually 1 to 18, in many cases 2 to 8, and a phosphoric acid esterrepresented by the formula (19):[R¹—O—(C₂H₄O)_(n−1)—C₂H₄O]_(m)—P(O)(OH)_(3−m)  (19)wherein R¹ is an alkyl group having usually 7 to 18 carbon atoms,especially 8 or 9 carbon atoms, n is an average addition mole number ofusually 1 to 18, in many cases 2 to 8, and m is an integer of 1 to 3. Asspecific examples of the phosphoric acid ester surface active agent,there can be mentioned that which are represented by the formula (20),for example, polyoxyethylene nonyl phenyl ether phosphate (for example,“LATEMUL”™ P-909 available from Kao Corporation):

 R: C₉H₁₉—C₆H₄O—O—(C₂H₄O)₈—C₂H₄—trialkyl phosphate represented by the formula (21) (for example,“PELEX”™ RP available from Kao corporation):

(iii) Alkali Metal Salt or Ammonium Salt of Phosphoric Acid Compound

(1) Primary Phosphate Salt

wherein M in an alkali metal such as Na or K, or an ammonium group. Thisdefinition for M is the same in the following formulae (23), (24) and(25).

(2) Secondary Phosphate Salt

(3) Tertiary Phosphate Salt

As a specific example of the secondary phosphate salt, sodiumdihydrogenphosphate represented by the formula (25) can be mentioned.

An alkali metal salt or ammonium salt of phosphoric acid compounds otherthan those recited above can be used. A mixed salt comprising aphosphoric acid compound to which both of an alkali metal end anammonium group have been bonded can also be used.

As specific examples of an alkali metal salt of the other phosphoricacid salt, there can be mentioned sodium metaphosphate represented bythe formula (26):

wherein n is usually in the range of 0 to 14, and, for example, whenn=4, this compound is sodium hexametaphosphate, and sodiumtripolyphosphate represented by the formula (27),

Further, as specific examples of the alkali metal salt and ammonium saltof a phosphoric acid compound, there can be mentioned potassiumphosphate, ammonium hydrogenphosphate, potassium pyrophosphate, sodiumpyrophosphate, potassium tripolyphosphate and sodium tripolyphosphate.

(iv) Compound Prepared by Introducing Ester Bond Plus Alkali Metal Bondor Ammonium Salt Bond into Phosphoric Acid Compound

(1) Dialkylphosphate Salt

wherein R is an alkyl, phenyl, alkylphenyl group or the above-mentionedhydrophobia group, and M is an alkali metal or ammonium group. Thesedefinitions for R and M are the same in the following formulae (29) to(33).

(2) Secondary Monoalkylphosphate Salt

These phosphate salts include, for example, potassium secondarymonoalkylphosphate represented by the formula (30):

and potassium dialkylphosphate represented by the formula (31):

The phosphate salts further include, for example, potassium 2-ethylhexylpyrophosphate and sodium 2-ethylhexyl pyrophosphate.

(v) Phosphine Compound

The phosphine compound includes, for example, a triphenylphosphinerepresented by the formula (32):(R)₃P  (32)such as triphenylphophine [(C₈H₈)₃P] and triethylphosphine [(C₂H₈)₃P].(vi) Hexaalkylphosphorus Triamide

The phosphorus-containing compound includes a hexaalkylphosphorustriamide represented by the formula (33):

When R is a methyl group, this compound is hexamethylphosphorustriamide.

Among the above recited phosphorus-containing compounds, phosphoric acidester surface active agents (usually used as a corrosion preventive),phosphoric acid compounds and alkali metal salts thereof a preferable.An alkali metal dihydrogenphosphate is especially preferable.

Compound (c)

Compound (c) is at least one compound selected from the group consistingof heterocyclic aldehydes, aromatic aldehydes and condensates of thesealdehydes, and includes, for example, heterocyclic aldehydes such asfurfural, 5-methylfurfural, 5-(hydroxymethyl)furfural,thiophenecarbaldehyde, nicotinic aldehyde and pyridoxal; aromaticaldehydes such as benzaldehyde, tolualdehyde, cuminaldehyde,phenylacetaldehyde, cinamaldehyde, phtalaldehyde, isophthalaldehyde andterephthalaldehyde; and condensates of these aldehydes. Of these,furfural and its condensate are especially preferable.

The ratio of compound (a) to compound (b) is usually in the range of1:10 to 100:1, preferably 1:5 to 80:1 and more preferably 1:2 to 70:1 byweight. The total amount of compound (a) plus compound (b) is usually inthe range of 0.1 to 2,000 ppm, based on the total weight of thehydrocarbon mixture containing a conjugated diene.

The amount of compound (c) is usually in the range of 0.001 to 10% byweight, based on the total weight of the hydrocarbon mixture containinga conjugated diene, The optimum amount of compound (c) varies dependingupon the particular highest temperature within a separating and refiningapparatus. For example, when the highest temperature is about 150° C.,the amount of compound (c) is preferably 0.5 to 5% by weight, and whenthe highest temperature is about 125° C., the amount of compound (c) ispreferably 0.01 to 0.1% by weight.

The procedure of using an anti-galling agent of the present invention isnot particularly limited, provided that the anti-gelling agent is usedin a state in which it is placed in contact with a conjugated diene or ahydrocarbon mixture containing a conjugated diene.

The anti-gelling agent of the present invention is preferably used in anapparatus for separating a hydrocarbon compound having two carbon atomssuch as ethylene from a hydrocarbon mixture containing hydrocarboncompounds having 2 to 9 carbon atoms such as ethylene, propylene,butene, butadiene and isoprene; an apparatus for separating ahydrocarbon compound having three carbon atoms such as propylene fromsaid hydrocarbon mixture; an apparatus for separating a hydrocarboncompound having four carbon atoms such as butadiene or butene from saidhydrocarbon mixture; an apparatus for separating a hydrocarbon compoundhaving five carbon atoms such as isoprene from said hydrocarbon mixture;and an apparatus for separating a hydrocarbon compound having ninecarbon atoms from said hydrocarbon mixture.

The anti-gelling agent of the present invention may contain, forexample, a polymerization inhibitor, a chain transfer agent or an oxygenscavenger, provided that a baneful influence is not exerted upon theobject of the present invention.

A method of preventing clogging according to the present inventioncomprises adding compound (a), compound (b) and compound (c) into anapparatus for separating and refining a hydrocarbon mixture containing aconjugated diene. Compound (a), compound (b) and compound (c) may beadded either after they are mixed together, or separately.

The apparatus for separating and refining a hydrocarbon mixturecontaining a conjugated diene includes, for example, an apparatus forseparating a hydrocarbon compound having two carbon atoms from ahydrocarbon mixture containing a conjugated diene; an apparatus forseparating a hydrocarbon compound having three carbon atoms from saidhydrocarbon mixture an apparatus for separating a hydrocarbon compoundhaving four carbon atoms from said hydrocarbon mixture; an apparatus forseparating a hydrocarbon compound having five carbon atoms from saidhydrocarbon mixture; and an apparatus for separating a hydrocarboncompound having nine carbon atoms from said hydrocarbon mixture.

The separating apparatus is equipped with a column such as adistillation column, an extractive distillation column or a strippingcolumn; a heat exchanger such as a condenser, a reboiler or a preheater;and a piping, a valve and other elements,

The position of an extractive distillation column or a distillationcolumn, at which compound (a), compound (b) and compound (c) are fedinto the extractive distillation column or the distillation column isnot particularly limited. These compounds (a), (b) and (c) are fed to,for example, a position higher than the raw material feeding stage, anupper side position to an extraction solvent-feeding stage of anextractive distillation column, an inlet or outlet of a condenserequipped on the top part of an extractive distillation column or adistillation column, or an inlet or outlet of a reboiler or a preheater.These compounds (a), (b) and (c) can be fed to the same position ordifferent positions.

As examples of the hydrocarbon mixture containing a conjugated diene tobe separated and purified by the anti-gelling agent of the presentinvention, there can be mentioned a petroleum fraction predominantlycomprised of C2 and C3 hydrocarbons such as ethylene and propylene,obtained by cracking of naphtha; a C4 petroleum fraction or a C5petroleum fraction obtained by separating C2 and C3 hydrocarbons fromthe petroleum fraction predominantly comprised of C2 and C3hydrocarbons; and C6 to C9 petroleum fraction obtained by separating C2to C5 hydrocarbons from the petroleum fraction predominantly comprisedof C2 and C3 hydrocarbons. As examples of the conjugated diene containedin the hydrocarbon mixture, isoprene and butadiene can be mentioned.

An embodiment of the anti-gelling agent and method of preventingclogging according to the present invention will now be describedspecifically with reference to the accompanying FIG. 1, FIG. 2 and FIG.3. FIG. 1, FIG. 2 and FIG. 3 are schematic diagrams illustratingapparatuses for separating-and-refining C4 fraction, C5 fraction and C2to C9 fraction, respectively, from a hydrocarbon mixture. A column suchas a distillation column, an extractive distillation column or astripping column; a heat exchanger such as a condenser, a raboiler or apreheater; and pipes, valves and other elements are not shown in thesefigures.

C2 Separation

In FIG. 3, a hydrocarbon mixture containing ethylene, propylene,isoprene and butadiene is fed through a pipeline 201 to an intermediatestage of a C2 separation column. An anti-gelling agent comprised ofcompounds (a), (b) and (c) is continuously fed through a pipeline 202 tothe C2 separation column. The C2 separation column is equipped with acondenser at the top thereof, whereby a part of the vapor is refluxedand the remainder is withdrawn through a pipeline 207 to recover a C2fraction. Refining of the C2 fraction gives refined ethylene.

C3 Separation

A fraction withdrawn from the bottom 208 is fed to an intermediate stageof a C3 separation column. An anti-galling agent comprised of compounds(a), (b) and (c) is continuously fed the C3 separation column. A C3fraction is withdrawn from the top of the separation column. Refining ofthe C3 fraction gives refined propylene.

C4 Separation

A fraction withdrawn from the bottom of the C3 traction column is fed toan intermediate stage of a C4 separation column (debutanizer), Ananti-gelling agent of the present invention is continuously fad througha pipeline 402 to the C4 separation column. A C4 fraction withdrawn fromthe top of C4 separation column is fed to an apparatus for separatingand refining the C4 fraction.

In FIG. 1, the C4 fraction is gasified and fed to an intermediate stageof a first extractive distillation column 101. An anti-gelling agent,prepared according to the recipe shown in Example 1, is continuously fedto an intermediate point of pipeline 102 to be thereby mixed withdimethylformamide. The anti-gelling agent-incorporated dimethylformamideis fed through line 102 into the first extractive distillation column101, and heated by a reboiler 105 equipped at the bottom part of column101, whereby a first extractive distillation is effected. Gas withdrawnfrom the top of column 101 is condensed by a condenser 103 and a partthereof is refluxed to the top of column 101. The remainder of gasmainly containing butane and butylene is withdrawn from a pipeline 104.The inner pressure of the first extractive distillation column isusually in the range of 1 to 10 atmospheres and the temperature of thecolumn bottom is usually in the range of 100 to 160° C. An extractedliquid comprised of butadiene and minor amounts of higher acetylene andarene hydrocarbons is withdrawn from the bottom of column. The extractedliquid is fed through a pipeline 106 to the top of a stripping column107, and is heated by a reboiler 109 at the bottom part of column 107 tobe thereby evaporated to effect distillation. The inner pressure ofstripping column 107 is usually in the range of 1 to 2 atmosphers andthe bottom temperature is a boiling point at the particular pressure.

Butadiene, higher acetylene and arena hydrocarbons are withdrawn fromthe top of stripping column 107, and liquefied by a cooler 108. A partof the liquefied material is allowed to flow back to the top of columnand the remainder is fed through a pipeline 120 to a water-washingcolumn 132.

An extraction solvent is withdrawn from the bottom of stripping column107, and circulated by a pump 110 through a cooler 111 and a pipeline102 to the first extraction distillation column 101.

Gas flowing out from the cooler 108 to fed through a compressor 112 anda pipeline 113 to an intermediate stage of a second extractivedistillation column 114. The above-mentioned anti-gellingagent-incorporated dimethylformamide is fed through a pipeline 130 tothe column 114. Diethylhydroxylamine is introduced through a pipeline160, provided immediately upstream to an inlet of a condenser 115. Theliquid is heated by a reboiler 117 equipped at the bottom part of columnwhereby second extractive distillation is effected.

The liquid withdrawn from the bottom of second extractive distillationcolumn 114 is fed to an intermediate stage of a recovering column 119. Adistillate from the top of recovering column 119 is fed through apipeline 121 to the compressor 112.

The liquid material withdrawn from the bottom of recovering column 119is fed through a pump 123 and a pipeline 124 to the top of a strippingcolumn 125. An extraction solvent is recovered from the bottom ofstripping column 125. A distillate withdrawn from the top of column isliquefied by a condenser 126 and a part thereof is refluxed to strippingcolumn 125, and the remainder is fed through a pipeline 131 to anintermediate of water-washing column 132.

Water is introduced through a pipeline 133 into water-washing column 132to refine an extraction solvent so that the extraction solvent isdehydrated to an extent such that it has a water content of 250 ppm inpipelines 102 and 130. The dehydrated extraction solvent flows through apipeline 138 where extraction solvents from pipelines 129 and 137 aremerged into the dehydrated extraction solvent, and the thus-combinedextraction solvent is circulated through pipelines 102 and 130 to firstand second extractive distillation columns 101 and 114, respectively.

Gas withdrawn from the top of second extractive distillation columnflows to a condenser 115 where the gas is condensed and a part thereofis allowed to flow back to the top of column. The remainder thereof iswithdrawn from pipe 116 and circulated to the top of first distillationcolumn (not shown in FIG. 1). A distillate discharged from the top offirst extractive distillation column 101 is condensed by a condenser anda part thereof is circulated to the column and the remainder is used asfuel for a boiler or burnt by a flare stack.

The material from the bottom of first distillation column in fed to anintermediate stage of second distillation column (not shown). Adistillate from the top of second extractive distillation column iscondensed by a condenser and a part thereof is allowed to flow back tothe column and the remainder is used an high-purity butadiene used, forexample, as a raw material for polybutadiene.

C5 Separation

In FIG. 3, a fraction withdrawn from the bottom of C4 separation columnis fed to an intermediate stage of a C5 separation column. Ananti-gelling agent of the present invention can be continuouslyincorporated through a pipeline 502 into the C5 separation column. A C5fraction is withdrawn from the top of C5 separation column. The C5fraction is fed to a separating-and-refining apparatus as illustrated inFIG. 2.

The C5 fraction is fed to a dimerization reactor for cyclopentane and afraction withdrawn from the reactor is fed to a pre-distillation columnto remove 1,3-pentadiene and dicyclopentadiene. Then, as shown in FIG.2, a fraction from the distillation column is fed through a pipeline 1to an intermediate stage of a first extractive distillation column A. Ananti-gelling agent of the present invention, prepared according to therecipe shown in Example 1, is added in a midway of a pipeline 2 to bethereby incorporated in dimethylformamide. The anti-gellingagent-incorporated dimethylformaide is fed through pipeline 2 to thefirst extractive distillation column A. The first extractivedistillation column A is equipped with a condenser 5 where a distillateis condensed and a part thereof is refluxed through a pipeline 6 and theremainder is withdrawn through a pipeline 7 as a fraction of pentane andpentene. A fraction from the bottom 8 of column A is fed to anintermediate stage of a first stripping colon B, and an extractionsolvent is recovered from the bottom 14 of column B.

A part of the fraction withdrawn from the top of first stripping columnB is circled through a pipeline 12 to the first stripping column B, andthe remainder of fraction is fed through a pipeline 13 to anintermediate stage of a first distillation column C. From the bottom ofcolumn C, 1,3-pentadiene and dicyclopentadiene are discharged.

A fraction (containing about 93% of isoprene) withdrawn from the top offirst distillation column C is fed through a pipeline 21 to anintermediate stage of a second extractive distillation column D.

The anti-gelling agent-incorporated dimethylformamide is fed through apipeline 23 to the second extractive distillation column D. A materialtaken from the bottom 29 of second extractive distillation column D isfed to an intermediate stage of a recovering column E. A fraction, takenfrom an intermediate stage positioned lower than the stage to which thematerial from the bottom 29 of column D is fed, in fed through apipeline 36 to an intermediate stage of a second stripping column F. Anextraction solvent is withdrawn from the bottom of recovering column Eand circulated. Acetylene and other fractions are withdrawn through apipeline 41 from the top of second stripping column. A part of adistillate from the top of recovering column E is condensed by acondenser 32, and a part of condensate is allowed to flow back torecovering column E and the remainder is circulated through a pipeline35 to second extractive distillation column D.

A distillate (containing about 99% of isoprene) withdrawn from the topof second extractive distillation column is fed through a pipeline 28 toan intermediate stage of a second distillation column H. Butyne-2 can betaken from the top of column H and high-purity isoprene can be takenthrough from the bottom of column H.

In FIG. 2, “I” shown in the lower part thereof is means for recoveringand refining an extraction solvent (dimethylformamide).

C9 Separation

A fraction taken from the bottom of a C5 separation column is fed to anintermediate stage of a C9 separation column, and a anti-gelling agentof the present invention is fed through a pipeline 902 to the C9separation column. A fraction used for gasoline material is withdrawnfrom the bottom of C9 separation column, and a fraction mainlycontaining B.T.X., i.e., benzene, toluene and xylene is withdrawn fromthe top of column.

The invention will now be described specifically by the followingexamples and comparative examples, but, the examples by no means limitthe scope of the present invention.

EXAMPLE 1

Refined isoprene with a purity of 99.3% was dissolved indimethylformamide to prepare 20 g of a 15% isoprene solution, Theisoprene solution was placed in a pressure-resistant glass vessel, and180 ppm of diethylhydroxylamine, 18 ppm of sodium dihydrogenphosphateand 2.5% by weight of furfural were added. Then 60 ppm of oxygen wasblown therein, and the vessel was closed and allowed to stand in anatmosphere maintained at 150° C. After seven days elapsed, the contentwas taken from the glass vessel and filtered.

The solid on a filter paper was vacuum-dried at 100° C. for 1 hour. Thedried solid is heroin referred to “polymer”. The polymer was dipped intoluene for 1 hour and the polymer solution was again filtered. Thesolid on a filter paper was vacuum-dried at 100° C. for 1 hour. Thedried product is herein referred to “gel”. The filtrate was vacuum-driedat 100° C. for 1 hour. The dried product is herein referred to“high-boil”.

The amounts of the polymer, gel and high-boil were measured, and theratios thereof to the amount of isoprene charged were determined. Theresults are shown in Table 1.

EXAMPLES 2 AND 3, COMPARATIVE EXAMPLES 1 to 6

The procedures described in Example 1 were repeated wherein kinds andamounts of compounds (a), (b) and (c) were varied as shown in Table 1with the other conditions remaining the same. The amounts of thepolymer, gel and high-boil were measured, and the ratios thereof to theamount of isoprene charged were determined. The results are shown inTable 1.

TABLE 1 Examples Comparative Examples 1 2 3 1 2 3 4 5 6 Compound (a)DEHAI (ppm) 180 180 180 — 200 — — — — Compound (b) Na-DHP (ppm) 18 — — —20 — — — — TNP (ppm) — 360 — — — — 400 — — PELEX (ppm) — — 360 — — — —360 — Compound (c) FF (wt. %) 2.5 2.5 2.5 — — — — — 3 Composition ofproduct (wt. %) Polymer 1.24 1.39 1.18 1.54 2.04 1.25 1.65 1.46 1.37High-boil 0.72 0.88 0.99 0.15 0.17 0.16 0.18 0.14 0.73 Gel 0.04 0.040.03 0.73 1.11 0.69 0.87 0.61 0.20 Note: Compound (a) DEHA =diethylhydroxylamine Compound (b) Na-DHP = sodium dihydrogenphosphateTNP = tris(nonylphenyl) phosphite PELEX = PELEX RP, available from KaoCorporation, sesqui-polyoxyethylene-2-ethylhexyl phosphate Compound (c)FF = furfural

EXAMPLE 4

Refined isoprene with a purity of 99.3% was dissolved indimethylformamide to prepare 20 g of a 15% isoprene solution. Theisoprene solution was placed in a pressure-resistant glass vessel, and180 ppm of diethylhydroxylamine, 3.6 ppm of sodium dihydrogenphosphateand 180 ppm of furfural were added. Then 180 ppm of oxygen was blowntherein, and the vessel was closed and allowed to stand in an atmospheremaintained at 125° C. After three days elapsed, the content was takenfrom the glass vessel. The amounts of the polymer, gel and high-boilwere measured, and the ratios thereof to the amount of isoprene chargedwere determined. The results are shown in Table 2.

EXAMPLE 5, COMPARATIVE EXAMPLES 7 AND 8

The procedures described in Example 4 were repeated wherein kinds andamounts of compounds (a), (b) end (c) were varied as shown in Table 2with the other conditions remaining the same. The amounts of thepolymer, gel and high-boil were measured, and the ratios thereof to theamount of isoprene charged were determined. The results are shown inTable 2.

TABLE 2 Examples Comp. Ex. 4 5 7 8 Compound (a) DEHAI (ppm 180 — — — NO*(ppm) — 180 — 200 Compound (b) Na-DHP (ppm) 3.6 3.6 — — Compound (c) FF(ppm) 900 500 900 — Composition of product (wt. %) Polymer 0.53 1.310.92 1.44 High-boil 0.22 0.18 0.21 0.13 Gel 0.01 0.04 0.35 0.97 Notes:Compound (a) DEHA = diethylhydroxylamine NO* =4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxy Compound (b) Na-DHP =sodium dihydrogenphosphate Compound (c) FF = furfural

Industrial applicability

By incorporating a small amount of an anti-gelling agent in ahydrocarbon mixture containing a conjugated diene, polymerization of theconjugated diene, especially gelling of polymer can be prevented, andstaining in an separation-and-refining apparatus, clogging of pipes, andreduction of heat efficiency in a condenser, a reboiler and others canbe avoided. Therefore, operation of the separation-and-refiningapparatus can be continued for a long period of time, and the operationcost is reduced.

The method of preventing clogging according to the present invention canbe advantageously employed especially in an extractive distillationapparatus and other distillation apparatuses.

1. An Anti-gelling agent for a hydrocarbon mixture containing aconjugated diene, which comprises (a) at least one compound selectedfrom the group consisting of compounds having an NO radical in themolecule, and precursor compounds capable or forming an NO radical, (b)a phosphorus-containing compound, and (c) at least one compound selectedfrom the group consisting of heterocyclic aldehydes, aromatic aldehydesand condensates of these aldehydes.
 2. An Anti-gelling agent for ahydrocarbon mixture containing a conjugated diene according to claim 1,wherein the conjugated diene is butadiene or isoprene.
 3. AnAnti-gelling agent for a hydrocarbon mixture containing a conjugateddiene according to claim 1, wherein the conjugated diene is isoprene. 4.An Anti-gelling agent for a hydrocarbon mixture containing a conjugateddiene according to claim 1, wherein compound (a) is at least onecompound selected from the group consisting of steric hindered nitroxylcompounds, steric hindered hydroxylamine compounds anddi-lower-alkyl-hydroxylamines.
 5. An Anti-gelling agent for ahydrocarbon mixture containing a conjugated diene according to claim 1,wherein compound (b) is a phosphoric acid ester surface active agent, aphosphoric acid compound or an alkali metal salt of a phosphoric acidcompound.
 6. An Anti-gelling agent for a hydrocarbon mixture containinga conjugated diene according to claim 1, wherein compound (b) is analkali metal dihydrogenphosphate.
 7. An Anti-gelling agent for ahydrocarbon mixture containing a conjugated diene according to claim 1,wherein compound (c) is a heterocyclic aldehyde or a condensate thereof.8. An Anti-gelling agent for a hydrocarbon mixture containing aconjugated diene according to claim 1, wherein compound (c) is furfuralor a condensate thereof.
 9. An Anti-gelling agent for a hydrocarbonmixture containing a conjugated diene according to claim 1, wherein theratio of compound (a) to compound (b) is in the range of 1:10 to 100:1by weight.
 10. A method of preventing clogging in an apparatus ofseparating and refining a hydrocarbon mixture containing a conjugateddiene, which comprises adding into the apparatus (a) at least onecompound selected from the group consisting of compounds having an NOradical in the molecule, and precursor compounds capable of forming anNO radical, (b) a phosphorus-containing compound, and (c) at least onecompound selected from the group consisting of heterocyclic aldehydes,aromatic aldehydes and condensates of these aldehydes.
 11. A method ofpreventing clogging according to claim 10, wherein the conjugated dieneis butadiene or isoprene.
 12. A method of preventing clogging accordingto claim 10, wherein the conjugated diene is isoprene.
 13. A method ofpreventing clogging according to claim 10, wherein saidseparating-and-refining apparatus is used for separating a hydrocarboncompound having two carbon atoms, a hydrocarbon compound having threecarbon atoms, a hydrocarbon compound having four carbon atoms, ahydrocarbon compound having five carbon atoms or a hydrocarbon compoundhaving nine carbon atoms, from the hydrocarbon mixture containing aconjugated diene.
 14. A method of preventing clogging according to claim10, wherein said separating-and-refining apparatus is used forseparating a hydrocarbon compound having four carbon atoms or ahydrocarbon compound having five carbon atoms from the hydrocarbonmixture containing a conjugated diene.
 15. A method of preventingclogging according to claim 10, wherein said separating-and-refiningapparatus is used for separating butadiene or isoprene from thehydrocarbon mixture containing a conjugated diene.
 16. A method ofpreventing clogging according to claim 10, wherein saidseparating-and-refining apparatus is used for separating a hydrocarboncompound having five carbon atoms from the hydrocarbon mixturecontaining a conjugated diene.
 17. A method of preventing cloggingaccording to claim 10, wherein said separating-and-refining apparatus isused for separating isoprene from the hydrocarbon mixture containing aconjugated diene.
 18. A method of preventing clogging according to claim14, wherein said separating-and-refining apparatus is an extractivedistillation apparatus for separating the respective hydrocarboncompound.
 19. A method of preventing clogging according to claim 14,wherein said separating-and refining apparatus is an extractivedistillation apparatus for separating the respective hydrocarboncompound by using dimethylformamide as an extraction medium.
 20. Amethod of preventing clogging according to claim 12, wherein the ratioof compound (a) to compound (b) is in the range of 1:10 to 100:1 byweight; and the total amount of compound (a) and compound (b) is in therange of 0.1 to 2,000 ppm and the amount of compound (c) is in the rangeof 0.001 to 10% by weight, based on the total weight of the hydrocarbonmixture containing a conjugated diene.
 21. A method of separating ahydrocarbon from a hydrocarbon mixture containing a conjugated diene bydistillation, characterized in that the distillation is carried out inthe presence of an anti-gelling agent comprising (a) at least onecompound selected from the group consisting of compounds having an NOradical in the molecule, and precursor compounds capable of forming anNO radical, (b) a phosphorus-containing compound.